Final answer:
Graded bedding in sedimentary rocks is most likely caused by the deposition of sediments from turbidity currents, which are underwater avalanches of sediment that move downslope.
Step-by-step explanation:
Graded bedding is a common sedimentary structure where a change in grain size can be observed within a single sedimentary bed. At the bottom of the bed are mainly coarse particles which get progressively smaller as you move vertically up the bed. Graded beds generally represent depositional environments in which transport energy decreases over time, like the changing water velocity in a river.
One of the most likely causes of graded bedding is the deposition of sediments from turbidity currents, which are essentially underwater avalanches of sediment that move downslope. As turbidity currents flow, they carry sediment of different sizes, with the larger particles settling at the bottom and the smaller particles staying suspended in the current and eventually settling on top.